KIVIMAKI, M. ... et al., 2015. Long working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603 838 individuals. The Lancet, 386(10005), pp.1739-1746.

Abstract:

Background Long working hours might increase the risk of cardiovascular disease, but prospective evidence is scarce,
imprecise, and mostly limited to coronary heart disease. We aimed to assess long working hours as a risk factor for
incident coronary heart disease and stroke.
Methods We identifi ed published studies through a systematic review of PubMed and Embase from inception to
Aug 20, 2014. We obtained unpublished data for 20 cohort studies from the Individual-Participant-Data Meta-analysis
in Working Populations (IPD-Work) Consortium and open-access data archives. We used cumulative random-eff ects
meta-analysis to combine eff ect estimates from published and unpublished data.
Findings We included 25 studies from 24 cohorts in Europe, the USA, and Australia. The meta-analysis of coronary
heart disease comprised data for 603 838 men and women who were free from coronary heart disease at baseline; the
meta-analysis of stroke comprised data for 528 908 men and women who were free from stroke at baseline. Follow-up
for coronary heart disease was 5·1 million person-years (mean 8·5 years), in which 4768 events were recorded, and
for stroke was 3·8 million person-years (mean 7·2 years), in which 1722 events were recorded. In cumulative
meta-analysis adjusted for age, sex, and socioeconomic status, compared with standard hours (35–40 h per week),
working long hours (≥55 h per week) was associated with an increase in risk of incident coronary heart disease
(relative risk [RR] 1·13, 95% CI 1·02–1·26; p=0·02) and incident stroke (1·33, 1·11–1·61; p=0·002). The excess risk of
stroke remained unchanged in analyses that addressed reverse causation, multivariable adjustments for other risk
factors, and diff erent methods of stroke ascertainment (range of RR estimates 1·30–1·42). We recorded a
dose–response association for stroke, with RR estimates of 1·10 (95% CI 0·94–1·28; p=0·24) for 41–48 working
hours, 1·27 (1·03–1·56; p=0·03) for 49–54 working hours, and 1·33 (1·11–1·61; p=0·002) for 55 working hours or
more per week compared with standard working hours (ptrend<0·0001).
Interpretation Employees who work long hours have a higher risk of stroke than those working standard hours; the
association with coronary heart disease is weaker. These findings suggest that more attention should be paid to the
management of vascular risk factors in individuals who work long hours.

Medical Research Council, Economic and Social Research Council, European Union New and Emerging
Risks in Occupational Safety and Health research programme, Finnish Work Environment Fund, Swedish Research
Council for Working Life and Social Research, German Social Accident Insurance, Danish National Research Centre
for the Working Environment, Academy of Finland, Ministry of Social Affairs and Employment (Netherlands), US
National Institutes of Health, British Heart Foundation.